The South China Morning Post has reported that China is planning to build an experimental hybrid fusion-fission reactor by 2030. The proposed reactor would be built at a military research facility in Sichuan province, and would use fast neutrons from fusion to burn u-238.

Reasons given for pursuing this concept are that China's sources of uranium are of a low grade, and its nuclear waste is stored on site. This reactor would be able to burn low-grade uranium and nuclear waste, and would extend the lifetime of China's uranium supply from about 100 years to several thousand years. The project may also have something to do with the announcement by Russia a year or so ago along the same lines. There are a few more details on China Daily Mail, but beyond that I haven't seen any details about the design.

The problem with fusion- fission- hybrids in the US is a funny one.
Fission supporters do not want to complicate their simple fission reactors with a complex fusion reactor.
Fusion supporters do not want a "dirty" fission reactor with their clean fusion reactor.
So hybrids like these, while having theoretically been possible for years, have not had a lot of support here.

The hybrid concept makes sense to me. Use those neutrons generated by the D-T fusion to fission U238. Not only do you get a lot more power. You eliminate the need for isotopic separation and you make use of those pesky neutrons.

paperburn1 wrote:On a similar note has anyone heard what the outcome of the thorium reactor test in Sweden has been? I think it's supposed to end sometime this year.

I guess you mean the five year experiments in Halden, Norway which will continue to 2017?

In 2013, the Norwegian technology company, Thor Energy, started an irradiation
programme in the Halden reactor aimed at qualifying thorium/plutonium fuel for
LWRs. This programme is overseen by the Norwegian Institute for Energy Technology
(IFE) at Halden, host of the NEA Halden Reactor Project. Instrumented test-rods
containing candidate thorium fuel specimens are currently undergoing irradiation
trials in the reactor, which is able to emulate PWR or BWR operating conditions. Key
properties of thoriated fuels such as thermal conductivity, or swelling and fission gas
release (FGR) as a function of burn-up are to be determined in these irradiation tests.
The trial operation of a commercial prototype thorium-MOX fuel in the Halden test
reactor is a significant step towards the broader use of thoria fuel for achieving “near-
term” fuel cycle goals, most notably with respect to minimisation of transuranics in
spent fuel.

As of 2015, the measured fuel temperatures are in accordance with known values for
the thermal conductivity of the respective materials. The centreline temperature of the
rods containing U-7Th fuel pellets is about 30-40 K lower than that of the pure UO 2
reference rod, indicating that the thorium dopant is improving the thermal conductivity
of the fuel pellet material, as expected. No FGR has been observed so far.
The test rig shown in Figure 4.1 will be complemented with a new instrumented rig
devoted to producing new irradiation data for (Th,Pu)O 2 fuel fabricated at IFE. Fabrication
trials using (Th,Ce)O 2 have been conducted in preparation for (Th,Pu)O 2 fuel pellet
production.
The thorium fuel manufacture and irradiation campaign will continue at least until
late 2017 and include several activities supporting the irradiation of LTRs – the next
required step in a thorium LWR fuel commercialisation programme. Among the suite of
PIE analyses foreseen are internal rod gas analysis (providing data on the release of
specific fission gases from the fuel ceramic), ceramography (showing how the fuel pellet
structure has changed over the burn-up period), advanced microscopy (for examining
elemental distributions within the irradiated fuel ceramic and for visualising various
radiation induced microstructures).

kurt9 wrote:The hybrid concept makes sense to me. Use those neutrons generated by the D-T fusion to fission U238. Not only do you get a lot more power. You eliminate the need for isotopic separation and you make use of those pesky neutrons.

But you need those pesky neutrons to breed the T used in the D-T reaction.

kurt9 wrote:The hybrid concept makes sense to me. Use those neutrons generated by the D-T fusion to fission U238. Not only do you get a lot more power. You eliminate the need for isotopic separation and you make use of those pesky neutrons.

But you need those pesky neutrons to breed the T used in the D-T reaction.

Doesnt the fission reaction itself produce Tritium as well? So you can share the neutrons between the two tasks, I guess.

I was wandering why fusion sourced neutrons. The mention of fisioning U238 answers that. So long as you are not trying to reach breakeven DT- fusion, I suspect there would be plenty of neutrons around for producing addition tritium from lithium and promoting uranium fission. I expect the fusion is a small part of the energy picture (actually costing energy). The fission fuel would presumably need to be less enriched, and the control system would use the fusion neutrons to push the fission to near super critical conditions, using the conrtol rods less (along with the less enriched fuel rods). This might be a little more safe as I again suspect control rod failure is not as serious. Stopping the fusion reaction also moves the fission pile away from criticality. I wonder though about the fission breakdown products and their continued heat production. This is the problem with almost all of the fission plant accidents- loss of coolent before or after shutdown. Would this approach change the dynamics of this dangerous fission product decay situation?

It seems like he key to make D+T hybrids work are neutron multipliers that produce multiple slightly lower energy neutrons from the (very) high energy neutrons from the D+T reaction.
That is at least to my best understanding of this.

Personally, I am wondering whether a fusion reactor design capable of a catalyzed D+D fusion at a high enough efficiency would not be the best option for such a hybrid reactor.
Helion is optimistic that their design can do pure D+D and D+He3 at a Q>1, so their design should theoretically be good for it.
Sorlox can do D+D as well (at a Q < 1 with their current prototypes). Maybe even their design (which is really compact) would be good enough for a hybrid.